The present invention relates to a novel milk coagulating microbial enzyme and to a method for its production.
Rennet, an enzyme that is obtained from the fourth stomach of sucking calves, is a very active milk coagulating agent. For this reason it has been and is now widely used for cheese-making. However, the increasing difficulties in obtaining raw material for rennet extraction, originated the actual search for substitutes of different origins.
Generally, proteolytic enzymes (proteases), whether of animal (pepsin, chemotrypsin, trypsin, catepsin, etc.) or plant origin (papain, ficin, bromelain, etc.) are characterized by coagulating activity. Furthermore, proteases produced by bacteria are also known as, for example, those elaborated by Pseudomonas fluorescens, Bacillus subtilis and Serratia marcescens. Some of these enzymes are able to cause a rennet-like coagulation in milk. However, their extremely high proteolytic activity impedes their use in cheese-making. In effect, the enzymes produced by these microorganisms cause the development of off-flavors in cheese, affect the consistency of the product, and develop excessively high amounts of acids by the very reason of their characteristically excessive proteolytic activity.
Furthermore it is also known that milk-clotting enzymes can be found in cultural broths of some fungi belonging to the genera Mucor (Mucor pusillus, Mucor rouxii and Mucor miehei) and Endothia (Endothia parasitica). Microbial rennet produced by some of the above mentioned species are presently used in cheese-making because of their reasonably low proteolytic activity.
However, it is not so far known that a milk-clotting enzyme advantageously utilizable on a commercial scale, can be found in the cultural broths of a group of microbes which are classified with the name of "yeasts" or Blastomycetes.
From a botanical standpoint it is very difficult to include yeasts in a single homogeneous group: they belong to the division Thallophyta of the Plant kingdom, lack chlorophyll, possess a definite cell wall and a nucleus, and lack any means of locomotion. These properties fit only one of the ten subdivisions of Tallophyta, namely the phylum Eumycophyta, or true fungi. However, botanists consider yeasts as rather primitive or degenerated forms of Eumycophyta. Their structural simplicity, almost total lack of mycelium, the formation of the ascus independently of the action of an ascogenous hypha system, and the total absence of ascocarps, and above all their monocellular life conditions, all make their systematic classification a difficult task.